Ammonium substitution in illite during maturation of organic matter

Lynda B. Williams, Ray E. Ferrell

Research output: Contribution to journalArticlepeer-review

74 Scopus citations


Pierre shale samples from a thin stratigraphic zone within the contact aureole of the lampro- phyric Walsen dike record changes due to thermal effects that are not influenced by detrital differences. Analyses of fixed-NH4, mineralogy, and Rock-Eval pyrolysis indicators of organic matter maturity provide new insights on the fixation process. Fixed-NH4 increases with the quantity of authigenic iUite formed from illite/smectite, but the maximum fixation per unit of illite formed occurs within the "oil window" where thermal breakdown of organic matter is rapid. Extrapolation of these results to the burial diagenetic regime supports the potential use of fixed-NH4 as an indicator of organic maturity and hydrocarbon migration pathways.

Original languageEnglish (US)
Pages (from-to)400-408
Number of pages9
JournalClays and Clay Minerals
Issue number4
StatePublished - Aug 1991
Externally publishedYes


  • Ammonium substitution
  • Fixed-ammonium
  • Hydrocarbon generation
  • Illite/smectite transformation
  • Organic maturation

ASJC Scopus subject areas

  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)


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